1. Field of the Invention
The invention relates to a fuel-saving drive recommendation system mounted on a vehicle equipped with a step-gear automatic transmission, and also to a fuel-saving drive recommendation method.
2. Description of the Related Art
Some of vehicles in recent years include a fuel-saving drive recommendation system described in Japanese Patent Application Publication No. 2007-138926 (JP-A-2007-138926). In the fuel-saving drive recommendation system described in JP-A-2007-138926, a recommended region for fuel-saving drive is set on the basis of various parameters, such as engine rotational speed, intake air flow rate, vehicle speed and accelerator operation amount, and, when the actual running state of the vehicle falls within the recommended region, a lamp is turned on to notify the driver that the fuel-saving drive is achieved. On the other hand, when the actual running state of the vehicle falls outside the recommended region, the lamp is turned off to notify the driver that the actual running state deviates from fuel-saving drive.
In addition, another fuel-saving drive recommendation system calculates a required driving force required for a vehicle and then determines whether the running state of the vehicle is a fuel-saving drive state on the basis of whether the calculated required driving force falls within a recommended region for fuel-saving drive. Then, such a fuel-saving drive recommendation system also notifies the driver of the result of determination in turning on or off of a lamp. Note that another fuel-saving drive recommendation system notifies a driver in bar indication, instead of notifying the driver of the result of determination as to whether the running state of the vehicle is a fuel-saving drive state in turning on or off of a lamp.
In the fuel-saving drive recommendation system described in JP-A-2007-138926, the above described parameters are used as parameters for determining whether the running state of the vehicle is appropriate for fuel saving.
On the other hand, some of vehicles in recent years employ so-called torque demand control. In the torque demand control, a required driving force of a vehicle driver is calculated to control engine output, or the like. To calculate such a required driving force, the speed ratio of a transmission, or the like, is also considered in addition to the above parameters. Therefore, the required driving force becomes a value that further conforms to engine output, that is, fuel consumption. Then, the required driving force is used as a parameter for determining whether the running state is suitable for fuel saving to thereby make it possible to further improve determination accuracy for fuel saving.
Incidentally, in the case of a step-gear automatic transmission, when the automatic transmission is in a low gear and the speed ratio (input shaft rotational speed/output shaft rotational speed) is high, driving force transmitted to a wheel side increases, so a margin of driving force increases. On the other hand, when the automatic transmission is in a high gear and the speed ratio is low, driving force transmitted to the wheel side decreases, so a margin of driving force decreases. For the above reasons, in the case of the step-gear automatic transmission, a difference in required driving force is set gear by gear, and a required driving force also varies as the gear is shifted. Therefore, when the above required driving force is used as a determination parameter in a fuel-saving drive recommendation system mounted on a vehicle equipped for a step-gear automatic transmission, there is a possibility that a driver experiences an uncomfortable feeling when the gear is shifted because of the following reasons, for example.
First, in the step-gear automatic transmission, when a gear instruction signal for shifting gears is changed, hydraulic pressures applied to a clutch and a brake are switched, so the engine rotational speed is regulated so that the input shaft rotational speed of the transmission becomes a rotational speed (synchronous speed) corresponding to the post-shift speed ratio. Thus, there is a certain delay from when the gear instruction signal is changed to when the actual engine rotational speed varies.
Here, when the gear instruction signal is changed as described above, the required driving force also varies, so the result of determination for fuel-saving drive also changes at the time when the gear instruction signal is changed. However, as described above, there is a certain delay from when the gear instruction signal is changed to when the actual engine rotational speed varies. In this case, the result of determination for fuel-saving drive changes ahead before the input shaft rotational speed of the transmission begins to vary, that is, before the engine rotational speed begins to vary. Therefore, the driver is notified of the result of determination for fuel-saving drive ahead before the driver experiences a variation in engine rotational speed, so there is a possibility that the driver experiences an uncomfortable feeling.